The present invention relates to an optical device and, more particularly, to an optical device having an optical component isolated from a housing.
A reflective or Bragg grating, which reflects light over a narrow wavelength band, can be established in an optical waveguide fiber (optical fiber) by known methods to produce a precise optical waveguide component that typically has channel spacings measured in nanometers. Such a fiber Bragg grating component can be used, for example, as a filter in a telecommunications system.
A change in the temperature of the grating region of the optical fiber can shift the central wavelength of the fiber Bragg grating component because of changes in glass refractive index and physical expansion of the fiber. Thus, the fiber Bragg grating component can exhibit wavelength variability over a range of operating temperatures. This temperature-induced variability can create practical difficulties in the use of the fiber Bragg grating component.
One method of passively athermalizing the fiber Bragg grating component involves changing the tension in the grating region of the optical fiber in response to temperature change. More specifically, since changing the tension in the grating region can shift the central wavelength of the fiber Bragg grating component, the central wavelength shift caused by temperature change can be offset by an appropriate change in the tension in the grating region.
This passive athermalization method can be implemented by attaching the optical fiber, under appropriate tension, to a substrate having a suitable negative temperature coefficient of thermal expansion. With a proper choice of design parameters, wavelength shift due to temperature change can be greatly reduced by an offsetting change in tension caused by a dimensional change in the substrate.
The fiber Bragg grating component is disposed in a housing to form an optical device in which the fiber Bragg grating component is protected from the environment. Conventionally, the substrate of the fiber Bragg grating component is connected directly to the housing by an adhesive covering an area on the substrate that averages about 80 square millimeters (mm2), but can vary from 40 to 400 mm2, with a thickness typically between 0.1 to 0.5 millimeters (mm).
Environmental testing, which involves monitoring the optical performance while cycling the temperature between xe2x88x9240xc2x0 C. and 85xc2x0 C., has shown that the central wavelength of the fiber Bragg grating component still shifts in an undesirable manner in response to temperature changes. This shift in the central wavelength may be caused, at least in part, by mechanical coupling of the substrate of the fiber Bragg grating component to the housing, which produces unwanted strain in the substrate when the housing undergoes dimensional changes caused by variations in ambient conditions, such as temperature and humidity.
An object of the present invention is to provide an optical device that solves the foregoing problems.
Another object of the present invention is to provide an optical device having a housing and an optical waveguide component that is substantially isolated or uncoupled from the housing.
Additional objects and advantages of the invention will become apparent from the description which follows. Additional advantages may also be learned by practice of the invention.
In a broad aspect, the invention provides an optical device including an optical waveguide component, a housing for the optical waveguide component, and a connecting portion that attaches the optical waveguide component to the housing while substantially completely isolating the optical waveguide component from force imposed on the connecting portion due to a dimensional change of the housing caused by a variation in ambient conditions.
In an additional aspect, the invention includes the method of making the inventive optical device, including the method of isolating the optical component.
It is to be understood that both the foregoing summary and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.